Converting colors

Update: I’m getting close. Now, the output colors are exactly half what they should be… If i put in
glColorf(90/255f, 40/255f, 133/255f)

It outputs R: 45 G: 20 B: 66

Now my code looks like this:

ByteBuffer pRGB = ByteBuffer.allocateDirect(12);


GL11.glReadPixels(x, 600-y, 1, 1, GL11.GL_RGB, GL11.GL_BYTE, pRGB);
    			
pRGB.rewind();

    			
System.out.print("R:");
System.out.print((pRGB.get()  & 0xff  ));
System.out.print("G:");
System.out.print((pRGB.get() & 0xff));
System.out.print("B:");
System.out.print((pRGB.get()  & 0xff));

OLD:
So I’m still working on color picking. Now the problem comes down to a color conversion problem. I set each primitive to a unique color using:

glColor3f(glColor[0]/255f,glColor[1]/255f, glColor[2]/255f) where glColor is an array of ints with each cell between 0 and 255.

Getting the pixel data looks like this:

//Disable anything that could affect color
GL11.glDisable(GL11.GL_TEXTURE_2D);
GL11.glDisable(GL11.GL_FOG);
GL11.glDisable(GL11.GL_LIGHTING);
GL11.glDisable (GL11.GL_BLEND);
GL11.glDisable (GL11.GL_DITHER);
GL11.glDisable (GL11.GL_TEXTURE_1D);
GL11.glShadeModel (GL11.GL_FLAT);
GL11.glClear(GL11.GL_COLOR_BUFFER_BIT | GL11.GL_DEPTH_BUFFER_BIT);


//Set up buffer to store pixel data
ByteBuffer pRGB = ByteBuffer.allocateDirect(12);
FloatBuffer fRGB = pRGB.asFloatBuffer();
    	    	

//Render primitives with unique color
RenderColors()




//Read pixel
GL11.glReadPixels( WindowWidth,WindowHeight-y, 1, 1, GL11.GL_RGB, GL11.GL_FLOAT, fRGB);
   
//Set buffer back to start 			
pRGB.rewind();
fRGB.rewind();

//Output pixel color    			
System.out.print("R:");
System.out.print((int)(pRGB.get() & 0xff));
System.out.print("G:");
System.out.print((int)(pRGB.get() & 0xff));
System.out.print("B:");
System.out.print((int)(pRGB.get() & 0xff));

Help?

I’m not sure if I got the point but, why are you using GL_FLOAT on glReadPixels if your color are set up using unsigned byte?

Shouldn’t this:

GL11.glReadPixels(x, 600-y, 1, 1, GL11.GL_RGB, GL11.GL_BYTE, pRGB);

Actually be:

GL11.glReadPixels(x, 600-y, 1, 1, GL11.GL_RGB, GL11.GL_UNSIGNED_BYTE, pRGB);

?

By the way, if performance is important for this you shouldn’t be using GL_RGB for your glReadPixels. Use GL_BGRA instead.

glColorf(90/255f, 40/255f, 133/255f)

You could just pass
glColor3uf(90,40,133);

you meant glColor3ub (instead of glColor3uf).

yeah !

Any other way besides using unsigned? I’m using Java, that isn’t an option.

just convert to signed :

int unsignedByteValue = 255;
byte signedByteValue;
if (unsignedByteValue >= 128 ) {
 signedByteValue = unsignedByteValue - 256;
} else {
 signedByteValue = (byte) unsignedByteValue;
}